Electromagnetic bell



June 17, 1930. J. F. MORAN ELECTROMAGNETIG BELL 1923 2 Sheets-Sheet lFiled May 12 l l l l L T .j

INVENTOR f/rz Moran BY M ATTORNE)l June 17, 1930. .A 1 F. MQRAN1,764,277

ELECTROMAGNET IC BELL Filed May 12, 1923 2 Sheets-Sheet 2 Patented June17, 19530 JOHN F. MORAN', OF JERSEY CITY, NEW JERSEY ELECTROMAGNETICBELL Application 1ed May 12,

The plunger is supported upon an integralV armn protruding from thelower end of the cover-yoke member. The gong is removably secured uponthe cover-yoke casting, and

substantially covers the same, a portion near the rim of the gong beingin the path of movement ofthe upper end of the plunger. The form electedfor the more specific claims hereof is a single stroke alternatingcurrent bell, but its novel features are closely inter-related withseveral other novel features and combinations, structural andfunctional, which, taken together, constitute a new standardized systemfor commercial installation ofall kinds of electric bells.

This bell embodies novel features where-Y by the rear casing whichserves as the outlet box or fixture is of a relatively small size suchthat its front is completely closed by the smallest bell which it isproposed to use as standard equipment. In order that such small sizeoutlet box may serve also as a rear casing for a large size alternatingcurrent bell the latter is made with itssolenoid coil and yoke of a sizepractically co-extensive with the area of the open face of the outletbox, while the plunger guide and support is pendant any desired distancebelow the outlet box, and the whole is covered by the larger size bellor gong which is then employed. This support element for the plungerguide andbell may be formed with 1923. Serial N'o. 638,475.

two independent bell-securing Iclamp elements, at different levels withrespect to the top of the plunger guide, so that bells of substantiallydifferent size may be employed, yet both present striking surfaces inexactly the same position with respect to the up-stroke of the plun er.

Functionally, this be l embodies novel electrical relations andreactions.

First: Alternating current bells, in the absence of special precautions,may give a second or third signal on one closure ofthe circuit,particularly, if the cycle of magnetism should be substantiallysynchronous with the return or drop of the plungerafw ter impact Withthe gong. I avoid such recurrent signal, by unbalancing the magneticlcircuit structure, substantially when the plun er is in gong-strikingposition, so as to e ect a preponderance of magnetic iiux toward oneside of the plunger, the latter tending thereby to move laterally foreffective braking thereof, until after the control circuit has beeninterrupted and the plunger has returned to its normal position.V In

the present specific application of this principle, the trailing endofthe plunger, which is normally beyond the magnetic circuit, ispreferably asymmetricahbeing cut away at one side thereof, so that whenit passes into the magnetic circuit upon impact with the gong, themagnetic attraction will be asymmetrical and will brake the plungermovement.

Second: A considerable number, as for in- 30 stance, eight or tenalternating current single-stroke bells of the solenoid and plunger coretype, may be used in series on the same circuit. ln such series use onan alternating current circuit,'the difficulty has 85 been that the timeconstant of response of the plungers of the different bells ispractically never the same for different bells of the same model. The'quickest plungers move into the magnetic field of their .sole

noids ahead of the others and choke the flow of current in the circuitincluding the solenoid coils of the slower bells, before the plungers ofthe latter can reach the powerful part of the fields of their respectivesolenoids. The result is that the slower plungers do not operate at all.

It has been proposed to obviate this difliculty by providing condensersto balance the inductance of the coils, but this is expensive. It hasalso been proposed to decrease the choking effect of the plunger withinthe coil by making the plunger very light but this result isineffective.

I accomplish the desired result by slowing down the time period ofresponse of all the plungers, preferably utilizing two factors. First,the initial position of the plunger core is pretty well outside of thefield of the solenoid so that the initial pull of said field isrelatively weak; and second, the plunger itself is preferably heavy. By

A utilization of these two expedients, I create a situation where apowerful current must be built up in the solenoid coil of all of thebells before any plunger moves. Then when the quickest plunger does moveit moves slowly and has a relatively long distance to travel before itgets in position to operate as a choke. The result is that, though someof the plungers are slower than others, they are all well under way ontheir operative stroke before any of them get to effective chokingposition. Moreover, they are then rapidly moving to positions where thesolenoid pull is amply sufficient to cause them to complete the stroke,notwithstanding the progressive choking inductance that each of themcontributes as its said stroke progresses.

In the accompanying drawings in which is shown one or more of thevarious possible embodiments of the several features of this invention,

Fig. 1 is a transverse sectional view of one embodiment of bell,

Fig. 2 is a plan view of the outlet box apart from the bell structure,

Fig. 3 is a view similar to Fig. 1 of a modified form of bell structure,and;

Fig. 4 is a sectional view taken along the line 4 -4 of Fig. 3.

Fig. 5 is a circuit diagram.

Referring now to Figs. 1 and 2 of the drawings, I have shown a bellstructure including a stamped metal outlet box 10, having a bottom 11,side and end walls 12 and a rim 13. The box is provided with the usualknock outs 14 which ma be punched out, as desired, for insertion o theconduits from the source of current. In the bottom or base of the outletbox is mounted an linsulating contact support 15, which may be of moldedinsulating composition and which is preferably secured to the base as byscrews 16, upstanding shields 17 integral with the support, preventingarcing over between said screws and the contiguous contact or terminalstrips 18 and 19, and an integral upstanding rib 20 between the twoterminal strips, preventing shortcircuiting, creeping or arcing overtherebetween. The terminal strips comprise rectangular pieces of metalembedded as at 21 within the molded composition, each bearing a pair ofscrews 22, one pair being connected to the source of current (not shown)and the other pair through conduits as at 23 to the solenoid 24 of thebell. Conductors 23 are clamped between a pair of insulating fibrestrips 25 and 26, best shown in Fig. 4, provided with correspondingregistering notches 27 in their contiguous edges and secured togetherand against the lower face of casting 28 as by screws 28a.

The casting 28 has an integral rectangular frame 29, which serves as aclosure for the outlet box removably clamped against the rim 13 thereofby screws 30 and threaded into transverse ledges 31 secured in theoutlet box. The casting in the preferred embodiment constitutes acombined magnet yoke and support for the solenoid 24, a carrier supportor guide for the solenoid plunger 32 and a mount for the gong 33. Thegong, as shown, is preferably removably secured as by a screw 34 upon anintegral stud 35 in the casting. The casting as shown in the drawings,includes a semi-cylindrical cavity 36 similar to that shown best in Fig.4 and in the under, concealed or enclosed side of the casting or cover,within which the solenoid 24 fits with relatively small clearance.

In the embodiment shown, a vertical insulating tube 37 extends throughthe axis of the solenoid 24 and is supported in corresponding apertures38, 39, and 40 respectively at the upper end of the yoke and at thelower end thereof, in an integral lug 41 depending from the lower edgeof frame 28, and below the yoke portion of the casting. The lower end ofthe tube 37 is preferably closed as by a plug 42 and is, moreover,secured in positlon by screw 43 extending transversely therethrough andthreaded into the frame 28 of the casting. The plunger 32 is an ordinarysoft iron cylindrical rod and is normally cushioningly supported upon ayielding felt wad 44 resting upon plug 42 in the guide tube. A resonantmetal striking tip 45 has a driving t in a corresponding socket 46 inthe upper end of the plunger, the rim of the gong 33 extending over theupper or open end of the tube 38 to be struck by said tip.

In operation, upon energizing the solenoid, say by direct current, theplunger 32 is drawn upward into the solenoid 24. As it rises it comesinto more effective range of the solenoid suction and accelerates untilit passeswhat may be termed the center of solenoidal attraction, afterwhich it overthrows, this is, travels by acquired momentum the shortremaining distance until the tip strikes the bell. The elastic reaction,down suction of the solenoid and gravity combine to cause rebound of theplunger, thus making the'blow on the bell a sharp, clean tap. While thecircuit remains closed, the plunger may oscillate up and down, but withdecreasing amplitude, and the bell will not be struck a ain until afterthe circuit has been 4opene and the plunger has fallen by gravity to theinitial position. The dropping of the plunger is effected withoutsubstantial vibration or jarring upon the parts, as it is cushioned bythe yielding wad 44.

In Figs. 3 and 4 is shown a modified form of construction. In thisembodiment, the casting 47 performs substantially the same functions asin Figs. 1 and 2, but is particularly designed for 7 use withl largergongs. The casting member here also has a closure frame 29 for theoutlet box 10, and a yoke for the solenoid 24, and has, furthermore, anintegral bracket arm 48 protruding in this case downward from the lowerouter edge of the yoke portion 48 and serving to sustain the plunger 49and the guide tube 50 therefor: More specifically, the tube 50, extendsthrough a corresponding aperture 51 in the lower end of'the bracket arm48, where it is secured in position as byI screw l52 and is vsupportedat its opposite end as at 53 by the upper end of yoke 49 and heldintermediate its ends in an aperture 54 through the lower portion of theyoke 48. rIhe gong 55 is supported upon the yoke casting as by screw 56at its center, and substantially covers thecasting, together with thebracket arm thereof, as shown. Fordirect-current operation, a plungergenerally similar to that shown in Fig. 1, but larg- A er, may be used.Other details need not be described, as they are substantially identicalwith the embodiment of Figs. 1 and 2 heretofore described, correspondingparts bearing identical reference` numerals.

The specific bell shown. in Figs. 3 and 4, although suitable for directcurrent operation, is more particularly designed for operation byalternating current.

The core is a relatively heavy plunger and,

in its rest position, only its upper end is within effective range ofthe lower end of the vsolenoid field. Hence it moves not at all until apowerful magnetic field has been built up in the solenoid by closure'ofthe circuit, but when it once starts, 1t accelerates very rapidly untilit reaches the center of attraction of the coil. Thereafter itoverthrows by momentum, deliversa sharp tap upon the gong, and leaves itimmediately,

case of alternating current, however, the rebound of the plunger is verylikely to synchronize with a succeeding reversal and rise of magnetism,due to reversal of the alternating current in the coil. In such casethere may be two or even three taps and rebounds before the oscillationof the plunger dies down to a point where the gong is no longer tapped.

According to my invention, the structure of the magnetic circuit isbroadly such that the initial magnetic pull on the plunger is directlyupward, but this automatically changes to a laterally unbalancedmagnetic pull upon the plunger during the upper part of its stroke,thereby bringing it into frictional engagement with the sides of theguide. The resulting braking effect begins just before the plungerstrikes the gong, but

due to the. inertia stored in the plunger in its long upward travel, itis not suiicient to materially affect the force of the blow on the gong.When the plunger drops after striking the gong, to its magnetically heldposition, the braking effect is sufficient to keep it from moving insynchronism with the variations in the magnetic field due to thefluctuations of the alternating current. In the preferred embodiment,this result is accomplished by the simple expedient of asymmetricallyreducing the cross-section of the pl'unger 49 at its lower end, that is,at the portion thereof initiallyV outside or beyond the circuit ofthemagnetic flux. To this end, the plunger may be cut away as at 57 at oneside and near the lower end thereof, so that the first or leadingportion will be symmetrical while the last or -follow portion will beasymmetrical.

-' vIn the operation of the plunger-magnet mechanism of Fig. 3,wherebythe damping 1y and may be shot approximately tothe gong 55,before its lowerk portion comes under appreciable energization. Duesolely to the axial asymmetry provided by the cut 57 over the lattersection of the core, bias of the magnetic field is established forsetting up derived or transverse stress According to the length and cut57, the time and abruptness of build-up on the plunger. character of theof the biasing stress may be controlled. Preferably, the asymmetrical*portion of the plunger should be short and the cut sloped, so that biasmay begin late in the stroke and then gradually increase in strength.When so applied, the effect of the bias will be negligible until reboundof the core from the gong, when the transverse drag will be ade quate tostay the plunger against excessive recoil and quickly bring it to restat its point of balanced suspension in the magentic field. Under thisarrangement for damping the plunger against oscillation, the speed ofthe stroke is not affected, and the efiiciency of the device istherefore not reduced, while the degree of bias automaticallyproportions to the longitudinal draw, under different current strengthsor changes of reluctance in the magnetic circuit. Therefore, the strikeris dependably restrained against oscillation or recurrent longitudinaleffects, thus insuringfbonafde single stroke operation of the gongirrespective of whether alternating current or direct current may beused for energizing the solenoid.

I have already described how, by making the plunger core heavy and itsupper end normally far down in the solenoid field, these bells may beused in series on an alternating circuit because the plunger cores startslowly during times of maximum magnetization, with the result that noneof them can operate quickly enough to get into current choking positionwithin the solenoid until the slowest member of the group is also wellstarted. The result is that the slowest bell strikes as surely as thequickest one. This important arrangement of my bells requires noillustration but for purpose of reference it is diagrammaticallyindicated in Fig. 5 where the bells a, b, c, d, e, f, g, and z, areindicated as being serially connected in the same circuit, the latterbeing energized from a suitable alternating current source, as G.

As before explained, one and the same size and type of outlet box ispreferably employed for mounting bells of all the various .sizes andtypes. To this end the large size bells are made so that the outlet boxfits only the upper solenoid-enclosing portion of said large size bell.The outlet box thus being suitable for the larger size bell, any smallerbell may be applied, down to and even below the size indicated in Fig.1.

The bracket arm 48 is preferably provided with an additional tapped hole58 for mounting thereat, in lieu of the gong 55, a larger gong (notshown), the structure being unaltered otherwise.

1. In a signal mechanism, a tubular coilto develop a longitudinalmagnetic field, a core coordinated with said coil to form aplunger-magnet, said core having axial asymmetry over the follow portionof its length for biasing said magnetic field.

2. In a signal mechanism, a tubular coil to develop a symmetricalmagnetic field about its axis, a plun er-core having its stroke throughsaid coiI, said plunger-core having axial asymmetry over the followportion of its length for effecting bias of said magnetic field to dampsaid plunger-core against oscillation following its stroke.

3. In an alternating current signal mechanism, a gong, a core to form aplungerstriker for said gong, a tubular coil to develop a longitudinalmagnetic field for acceleratedly drawing said core, said core havingaxial asymmetry over a limited portion of its following length2 toderive transverse stress from said magnetic field for restraining saidcore against oscillation subsequent to its striking said gong. I

4. In a signal mechanism, a gong, a tubular coil to provide alongitudinal magnetic field, a plunger-core for said coil to strike saidgong, said core being axisymmetric over more than two-thirds of theleading portion of its length for passive response to the longitudinaldraw of said magneticl field, while the remainder of said core isaxially asymmetric to effect bias of said magnetic field for stressingsaid core against oscillation following a single blow to said gong.

5. In a plunger magnet for alternating current, a tubular coil, a pluner acceleratedly drawn by said coilA to eect a single stroke, saidplunger being axisymmetric over the leading and greater portion of itslength to render it passively responsive to longitudinal magnetic drawof said coil, the remainder of said plunger being so designed thatwholly due 'to its configuration bias of said longitudinal magnetic drawwill be accomplished for quickly bringing said plunger to rest followinga stroke thereof.

6. In an alternating current signal mechanism, gong means, a striker forsaid gong means, a tubular coil to develop a longitudinal magneticfield, a carrier for said striker comprising a core for said coil. inthe form of a plunger acceleratedly attracted by said magnetism, saidcore being proportioned over the first and greater section of its lengthto render it passively responsive to the longitudinal draw of saidmagnetic field, the remaining section of said core being proportioned toaccomplish biasing of said magnetic field for restraining said coreagainst excessive recoil after strikin said gong.

I. In a plunger magnet for alternating current, a gong, a plungerstriker for said gong, a tubular coil developing a longitudinal magneticfield acceleratedly to impel said plunger-striker for delivering a blowto said gong, the first and greater portion of the length of saidplunger being formed axisymmetric to render it free and passivelyresponsive longitudinally to said magnetic field, the last and leastortion of the length of said plunger being ormed axially asymmetric in amanner to eiect a slow-to-buildup bias of said magnetic field forstressing said plunger against recurrent striking of said gong followingdelivery of a single blow thereto.

Signed at New York 'city in the countyof New York and State of New Yorkthis 10th day of May A. D. 1923.

JOHN F. MORAN.

